the mammalian nervous system

• a successful organism must be able to respond to changes in the environment, these changes could be in the internal or external environment. A communication system for a successful organism must:

  Detect changes in environment

  make suitable responses

  coordinate a range of effectors to carry out responses to a stimulus.
• what are the divisions of the nervous system?

  Central nervous system (CNS) and peripheral nervous system (PNS). The PNS is divided into the sensory system and motor system. The motor system is divided into the somatic and autonomic system.
• the central nervous system consists of the brain and spinal cord. The human brain consists of about 86 billion nervous systems. much of the brain composes of relay neurons which have multiple connections enabling complex neural pathways. most of these cells are non myelinated and as such they look grey in colour- this is grey matter. The spinal cord contains large numbers of myelinated neurons that make up an outer region of white matter. these myelinated neurons carry action potentials up and down the spinal column.
• the role of the peripheral nervous system is to ensure rapid communication between the sensory receptors, the central nervous system and the effectors. The peripheral nervous system is composed of sensory and motor neurons, usually bundled together in a connective tissue sheath to form nerves.
• the sensory fibres entering the central nervous system are dendrons of the sensory neurons. These neurones conduct action potentials from the sensory receptor into the central nervous system. These neurones have their cell body inside of the dorsal root leading into the spinall cord and a short axon connecting to other neurons in the central nervous system.
• the somatic nervous system consists of motor neurons that conduct action potentials from the central nervous system to the effectors that are under voluntary control, such as the skeletal muscles. These neurons are mostly myelinated so responses can be rapid. There is always one single motor neuron that connects the central nervous system to the effector.
• the autonomic nervous system consists of motor neurons that conduct action potentials from the central nervous system that are not under voluntary contreo. This includes glands, cardiac muscle and smooth muscle in the walls of blood vessels, the airways and the wall of the digestive system. The control of many of these effectors does not require rapid responses and the neurons are mostly non myelinated. there are at least 2 neurons involved in the connection between the central nervous system and the effector, these neurons are connected at small swellings called ganglia.
• Autonomic means self-governing, and the autonomic nervous system operates to a large extent independently of conscious control. It is responsible for controlling the majority of the homeostatic mechanisms and so plays a vital role in regulating the internal environment of the body.
• the autonomic nervous system can be further divided into the sympathetic system that prepares the body for activity and the parasympathetic system that conserves energy. The sympathetic and parasympathetic systems differ in structure and action. they are antagonistic systems, as the action of one system opposes the action of the other. In general, at rest, action potentials pass along the neurons of both systems not very frequently.
• what are the effects that the sympathetic nervous system could bring?


  Increased heart rate

  dilated pupils

  increased ventilation rate

  reduced digestive activity

  orgasm
• what are the effects that the parasympathetic system can bring?


  Decreased heart rate

  constricted pupils

  reduced ventilation rate

  increased digestive activity

  sexual arousal
• how does the sympathetic system differ from the parasympathetic system?


  Consists of many nerves coming out of the CNS to a separate effector

  ganglia outside of CNS

  short pre ganglionic neurones

  long post ganglionic neurones, depending on where the effector is

  noradrenaline is used as the effector

  increased activity- body is prepped for activity

  most active in times of stress
• how does the parasympathetic system differ from the sympathetic system?


  Consists of a few nerves leading out of the CNS, dividing and leading to seperate effectors

  ganglia are in the effector tissue

  long pre - ganglionic neurones, dependent on the position of an effector.

  short post ganglionic neurones

  uses acetylcholine as the neurotransmitter

  decreases activity, conserves energy

  most active when sleeping or relaxing